1. Field of the Invention
This invention relates to a cam gear controlling mechanism, and more particularly to a controlling mechanism including a cam gear which has a cam portion and a gear portion which has a toothed portion and a non-toothed portion.
2. Description of the Prior Art
A controlling mechanism of the type which includes a cam gear is conventionally used to control the position of a movable member which is selectively moved to one of a plurality of control positions to establish a desired one of a plurality of control modes.
A controlling mechanism of the type mentioned is basically constructed so that it comprises a cam gear having a gear portion on which a plurality of non-toothed portions are formed individually corresponding to the controlling positions of such movable member and a controlling cam portion for pressing the movable member when the cam gear is rotated, a driving gear for rotating the cam gear when it is engaged with the gear portion of the cam gear, a pivotal trigger lever, electromagnetic means for controlling the trigger lever, initially rotating means and lever returning means. The cam gear has a plurality of stopper portions in sections thereof in which the non-toothed portions are opposed to the driving gear while an engaging projection for engaging with such stopper portions is provided on the trigger lever. While the trigger lever is attracted to the electromagnetic means, it is held at an arresting position at which the engaging projection thereof is positioned on a locus of rotation of the stopper portions, but when such attraction of the trigger lever by the electromagnetic means is cancelled, the engaging projection thereof is moved to a non-arresting position displaced from such locus of rotation.
The controlling mechanism operates in the following manner. In particular, the controlling mechanism normally establishes one of a plurality of modes wherein one of the non-toothed portions of the cam gear is opposed to the driving gear and a corresponding one of stopper portions of the cam gear is abutted with the engaging projection of the trigger lever to stop rotation of the cam gear while the movable member is held at one of the control positions. Then, if the attraction of the trigger lever to the electromagnetic means is cancelled to allow the trigger lever to be moved to a non-arresting position, then the cam gear is once rotated by the initially rotating means to an engaging position at which a next one of the toothed portions to the non-toothed portion which has been opposed to the driving gear till then engages the driving gear. Consequently, the cam gear is now rotated, from the engaging position, by the driving gear. During such rotation of the cam gear, the controlling cam portion thereof presses the movable member toward another control position while the trigger lever is returned to the arresting position by the lever returning means. Then, when the cam gear is rotated to a position at which a next non-toothed portion is opposed to the driving gear, another one of the stopper portions is abutted with the engaging projection of the trigger lever to stop rotation of the cam gear. Meanwhile, the movable member is moved to and thereafter held at another control position to establish another control mode.
As described above, a controlling mechanism of the type which includes a cam gear requires initially rotating means for rotating the cam gear to its engaging position when attraction of the trigger lever is cancelled in a certain control mode and lever returning means for returning the trigger lever to its arresting position at least for a period of time after the cam gear is moved to the engaging position until a next non-toothed portion is opposed to the driving gear.
Such initially rotating means is constructed in most cases so that the movable member is normally urged by a resilient force of resilient means and at whichever control position the movable member is, when the movable member presses the controlling cam portion of the cam gear under the resilient force of the resilient means, a turning force is applied to the cam gear so as to rotate the cam gear by some rotational angle. Meanwhile, the lever returning means in most cases is constructed as another cam means which is rotated by the cam gear to return the trigger lever from the non-arresting position to the arresting position.
Since the conventional controlling mechanism of the type including a cam gear has a large number of parts in this manner, it has a problem that it is complicated in construction and requires a great spacing for the arrangement of the parts. Further, since initial rotation of the cam gear is provided by initial movement of the movable member in a certain direction from the controlling position, it often occurs that the direction of such initial movement thereof must be set reversely to the direction of movement thereof to a next controlling position. Consequently, the controlling mechanism is disadvantageous in that much time is required for such movement of the movable member and setting of the controlling positions and/or strokes of movements is complicated.
On the other hand, as a mechanism for controlling the position of a movable member which is moved between two different positions, an electromagnetic operating mechanism is known which includes a magnetic attracting member such as a permanent magnet and a movable element slidably movable toward and away from the magnetic attracting member such as, for example, a solenoid plunger having a movable iron core.
An exemplary one of such conventional electromagnetic operating mechanisms is shown in FIG. 1A. Referring to FIG. 1A, the electromagnetic operating mechanism shown is generally denoted at a and includes a solenoid plunger b of the self-holding type including a permanent magnet c, a movable iron core e supported in a coil bobbin d for sliding movement toward and away from the magnet c and a coil f wound on the coil bobbin d. A movable member g is connected to the movable iron core e such that it is moved between a first position shown in FIG. 1A and a second position shown in FIG. 1B. The movable member g is normally biased toward the second position by resilient means not shown, and when it is pushed to move to the first position, the movable iron core e of the solenoid plunger b is attracted to the magnet c. Consequently, even if the force to urge the movable member g toward the first position disappears after then, the movable member g is held at the first position. On the other hand, if the coil f is energized in this condition, then the attraction of the movable iron core e by the magnet c is cancelled by a magnetic force produced from the coil f to allow the movable member g to be moved to the second position by the resilient means not shown.
In such electromagnetic operating mechanism a, connection between the movable iron core e and the movable member g is established in most cases by a connecting pin h provided on the movable member g and inserted in a connecting hole i formed in the movable iron core e.
By the way, in order to assure smooth movement of the movable iron core e and the movable member g of such electromagnetic operating mechanism a, the movable member g must necessarily press the movable iron core e in a direction parallel to the direction of movement of the movable iron core e. With such construction of the movable member g and the movable iron core e, a moment can be prevented which may otherwise act in a direction different from the direction of movement of the movable iron core e, and consequently, smooth movement of the movable iron core e and the movable member g can be assured.
Actually, however, it very seldom occurs that, after assembly of the electromagnetic operating mechanism a is completed, the direction in which the movable member g presses the movable iron core e, or more particularly, the direction in which the connecting pin h presses an inner face of the connecting hole i, is just in parallel to the direction of movement of the movable iron core e. Rather, it is more common that, due to tolerances in working accuracy of various portions of the movable member g or in accuracy in mounting of the movable member g and/or the solenoid plunger b and so forth, an axis of the connecting pin h and the inner face of the connecting hole i do not extend in parallel to each other, or even where the axis of the connecting pin h and the inner face of the connecting hole i extend considerably in parallel to each other, the direction itself of movement of the movable member g is inclined with respect to the direction of movement of the movable member g. In such condition, generally a location at which the connecting pin h presses the inner face of the connecting hole i will be displaced along the axis of the connecting pin h. Consequently, part of a force of the connecting pin h pressing the inner face of the connecting hole i acts as a vector in a direction perpendicular to the direction of movement of the movable iron core e. As a result, a loss takes place in the force of the movable member g pressing the iron core e while the movable iron core e is acted upon by a moment in a direction different from the direction of movement thereof, which will cause a so-called pinch between the movable iron core e and the inner face of the coil bobbin d.
Since such loss of a pressing force or pinch makes movement of the movable iron core e and the movable member g heavier, a malfunction may be caused such that the timing of movement of the movable member g is delayed or the movable member g is not moved to a predetermined position.
Further, if the movable iron core e is contacted with the magnet c while it remains in an inclined condition, then opposing faces of the magnet c and the movable iron core e are not closely contacted with each other and the movable iron core e is thus attracted to the magnet c in a condition wherein it is not contacted fully with the magnet c. In such attracted condition, the attracting force of the magnet c acting upon the movable iron core e is so low that, when some external force or shock acts, the movable iron core e may be removed readily from the magnet c.
Further, some tolerances cannot be avoided from accuracy in dimension of various portions of movable member, solenoid plunger, means for moving the movable member toward the solenoid plunger and so forth and also in dimension of mounting positions of those member, and some dispersion takes place in stroke of movement of the movable member among different electromagnetic operating mechanisms as products due to such tolerances. Consequently, even if the movable member comes to the attracted position, the movable iron core may not be contacted with the magnet.
Therefore, with a conventional electromagnetic operating mechanism of the type described above, a resilient portion having a so-called limiter function is frequency provided on the movable member so that some overstroke may be provided to an amount of movement of the movable member when the movable member is to be moved to the attracted position. For example, a resilient arm is formed on the movable member such that it may have a flexible elasticity in a direction of movement of the movable iron core so that the movable member is pressed toward the attracted position by way of the resilient arm while the stroke for such pressing operation is set a little greater than a stroke necessary for the movable member to come to the attracted position so as to provide an overstroke. Thus, the movable member is resiliently pressed against the solenoid plunger by the resilient force of the resilient arm in the overstroke. Consequently, the movable iron core is contacted with certainty with the magnet.
In this manner, with the conventional electromagnetic operating mechanism, since limiter means is provided on the movable member such that pressing by the pressing means to move the movable member to the attracted position may be performed by way of the resilient means and besides an overstroke is provided to such pressing operation, it is disadvantageous in that the movable member is complicated in construction or is great in size. Further, since the shapes, positions and so forth of the pressing means and the resilient portion are restricted from each other, it is also disadvantageous in that designing of shapes of various portions, layout of various members and so forth are very difficult.